1. Field of the Invention
The present invention relates to self-aligned contacts and a method of forming the same. More particularly, the present invention relates to a self-aligned buried contact pair and a method of forming the same.
2. Description of the Related Art
Recently, a trend toward smaller design rules for semiconductor devices, such as gigabit dynamic random access memory (DRAM) devices, has advanced to such an extent that it is highly difficult to secure an alignment margin when aligning a buried contact with a bit line semiconductor layer or an interconnect layer underlying the buried contact. A misalignment of the buried contact and bit line causes a fail of the contact resistance.
Further, as a design rule decreases, a conventional lithography method is no longer acceptable. Specifically, when a design rule is greater than 0.11 μm, conventional lithography using a KrF light source having a wavelength of 248 nm is acceptable. When a design rule is less than 0.11 μm, however, lithography using an ArF light source having a wavelength of 193 nm must be used. Thus, as the design rule deceases, the wavelength of the light source used in the lithography process must decrease.
Significant differences exist between KrF and ArF lithography. For example, because the two different lithographic processes use different light sources, different photoresists must be used. The ArF lithography process requires a more sensitive photoresist that has a poor etching immunity. Accordingly, more ArF photoresist is consumed during an etching process and thus, an initial thickness of the ArF photoresist must be greater than what is used in connection with a KrF lithography. Resultantly, having to use ArF lithography is a costly consequence of the reduction of the design rule.